The present invention relates to a liquid ink for selective printing. More particularly, it relates to a liquid ink for selective printing endowed with a fungus resistance.
Generally, a liquid ink for selective printing for use in printing media such as ink ribbon and ink roller contains a non-drying oil as a main component of the vehicle thereof.
Printing media such as ink ribbon and ink roller are liable to get moldy due to ink components, contaminants, dusts and moisture attached thereto, and the like.
A general means for the prevention of mold growth is to use an antifungal agent. However, it was found that when a usual antifungal agent was simply added to a selective printing liquid ink, the ribbon impregnated with the liquid ink was lowered in printing durability. Printing durability means the number of characters printed until the optical density of printed characters falls to the prescribed lower limit in the case of conducting a continuous printing using the same ink ribbon.
By the elucidation of the cause of the above phenomenon, it has been found that a selective printing liquid ink to which an antifungal agent is added gels on storage or assumes a thixotropic property though the ink does not cause gelation, which results in lowering the flowability of the ink. Hereinafter the above two phenomena, the gelation and the possession of thixotropic property are referred to collectively by the term "gelation". In particular, it has been found that when a printer is operated continuously, the internal temperature rises to 60.degree. to 70.degree. C. and the gelation of the ink is accelerated by such a high temperature condition.
An object of the present invention is to provide a selective printing liquid ink which has an excellent fungus resistance and does not impair the printing properties of printing media using the liquid ink as a result of storage.
This and other objects of the invention will become apparent from the description hereinafter.